U.S. Pat. No. 7,626,500 entitled Security Display With Central Control System assigned to InVue Security Products Inc. of Charlotte, N.C. describes a pseudo line alarm system in which each display module 15 and sensor 25 combination is electrically connected to a common power supply 5 and to a common central alarm unit 9. The common power supply 5 provides power from an external source (e.g. 120V AC outlet) to each display module 15 and sensor 25 at a predetermined operating power (i.e. voltage and/or current) via a power transformer 23 that may be provided by the OEM of the item of merchandise 3 being displayed at the Display Position. In this manner, each display module 15, sensor 25 and item of merchandise 3 at each Display Position is electrically connected in parallel to the power supply 5, and again in parallel to the central alarm module 9.
The central control system shown and described in the InVue U.S. Pat. No. 7,626,500 is particularly advantageous for displaying various items of merchandise having different operating power requirements using the power cables and transformers provided by the OEM of the item of merchandise. However, the capacity of the system is limited by the number of input jacks (ports) available on the central alarm module 9. It is possible to utilize one of the open ports to electrically connect another central alarm module 9 having additional ports to the system in a “daisy chain” manner. However, routing each of the cords 17 from the plurality of display modules 15 (with or without another central alarm module) to the ports of the central alarm module 9 introduces cord management issues, as well as potential cross talk and electrical interference concerns. Accordingly, management of the system, as well as the aesthetics of the merchandise display, can become problematic with only a few Display Positions installed.
Historically, line alarm systems use an electrical sense line or “sense loop” to detect the presence of an item of merchandise attached to a security device by means of a sensor (e.g. limit, proximity, etc.) switch disposed between the security device and the item of merchandise. The sense loop produces a binary ON/OFF alarm signal. A problem with conventional sense loop methodology is that a separate electrical circuit is routed in parallel from the alarm module to each sensor switch. Line alarm systems using the parallel routing method are more accurately described as “octopus” systems than “line alarm” systems since the sense loop cabling for each Display Position runs from the security device back to the central alarm module. A detriment of the parallel routing method is that the additional cabling required can utilize all of the available space under the display counter with only a few Display Positions installed. Alternatively, a single electrical circuit may be routed in series from the alarm module to all of the sensor switches. A detriment of the series routing method is that when the security device at one Display Position is disarmed (turned off), the security device at each of the other Display Positions is also disarmed. Both the parallel routing method and the series routing method lead to an undesirable condition if a retailer chooses to shut off the entire line alarm system, for example when one or more Display Positions are repeatedly false alarming, when maintenance is being performed, or when the retailer removes an item of merchandise from a Display Position to allow a customer to examine and operate the merchandise without the burden of the sensor cable (tether). When an entire line alarm system is turned off, it is oftentimes accidentally, or even intentionally, not turned back on.